The purpose of this study is to determine whether plasma exchange is effective in reversing the neurological injury in patients with acute, severe inflammatory demyelinating disease. The study is randomized, sham exchange, controlled, and double marked. Patients who do not improve to a moderate or marked degree in the first 14 days of treatment phase cross-over to the appropriate treatment. The study was completely enrolled as of 10/98. The final patient in the study completed the treatment phase in 11/98 after which the PI became unblinded to the treatment assignment and study results. The primary analysis was positive. Moderate to marked improvement occurred in 42% of patients who underwent active treatment versus 6% who underwent sham exchange. The primary analysis was positive (p=0.011). Secondary outcome measures were also positive in support of treatment benefit or showed strong trends. Treatment benefit or evident early after active treatment was initiated in responders and was sustained over six months follow-up. The results have been submitted for publication and are in the review process. Extensive studies analyzing serum samples collected prospectively are in progress to determine factors that are associated with response to treatment.